Photographers consider themselves lucky when they catch a green flash. The sunset emerald ray is so rare, it was once thought to be a fable. Now imagine the odds of catching a triple green flash. James W. Young did it last night while standing on Oregon's Cannon Beach:

"The setting sun produced a green flash which split into three layers," marvels Young. "I photographed them using a 1120mm telephoto lens with a Canon 1Dx Mark II camera."
This is a sign of very strong temperature inversions (warm air above cold) over the Pacific Ocean. Strong inversions produce 'ducts'. Rays from the setting sun get trapped in these ducts, bouncing up and down and traveling long distances in layers sometimes only a few inches thick. A trio of ducts split the green flash into a stack of three. You can actually see the ducts edge-on in Young's picture--a marvel, indeed.
https://spaceweather.com/

September 20, 2021 / Dr.Tony Phillips - NASA

Sept. 24, 2021: No solar storms? No problem. Earth has learned to make its own auroras. New results from NASA’s THEMIS-ARTEMIS spacecraft show that a type of Northern Lights called “diffuse auroras” comes from our own planet – no solar storms required.

Diffuse auroras look a bit like pea soup. They spread across the sky in a dim green haze, sometimes rippling as if stirred by a spoon. They’re not as flamboyant as auroras caused by solar storms. Nevertheless, they are important because they represent a whopping 75% of the energy input into Earth’s upper atmosphere at night. Researchers have been struggling to understand them for decades.

Above: Diffuse auroras and the Big Dipper,
photographed by Emmanuel V. Masongsong in Fairbanks, AK

“We believe we have found the source of these auroras,” says UCLA space physicist Xu Zhang, lead author of papers reporting the results in the Journal of Geophysical Research: Space Physics and Physics of Plasmas.

It is Earth itself.

Earth performs this trick using electron beams. High above our planet’s poles, beams of negatively-charged particles shoot upward into space, accelerated by electric fields in Earth’s magnetosphere. Sounding rockets and satellites discovered the beams decades ago. It turns out, they can power the diffuse auroras.

The video below shows how it works. The beams travel in great arcs through the space near Earth. As they go, they excite ripples in the magnetosphere called Electron Cyclotron Harmonic (ECH) waves. Turn up the volume and listen to the waves recorded by THEMIS-ARTEMIS:

Above: A great electrical circuit in space powering diffuse auroras. ECH waves were sonified by NASA’s HARP (Heliophysics Audified: Resonances in Plasmas) software.

ECH waves, in turn, knock other electrons out of their orbits, forcing them to fall back down onto the atmosphere. This rain of secondary electrons powers the diffuse auroras.

“This is exciting,” says UCLA professor Vassilis Angelopoulos, a co-author of the papers and lead of the THEMIS-ARTEMIS mission. “We have found a totally new way that particle energy can be transferred from Earth’s own atmosphere out to the magnetosphere and back again, creating a giant feedback loop in space.”

According to Angelopoulos, Earth’s polar electron beams1 sometimes weaken but they never completely go away2, not even during periods of low solar activity. This means Earth can make auroras without solar storms.

The sun is currently experiencing periods of quiet as young Solar Cycle 25 sputters to life. Pea soup, anyone?  [Note: Solar Cycle 25 is accelerating.  MS}

End Notes:

(1) Why do these electron beams exist? Earth’s magnetosphere is buzzing with energetic particles. Many of them are captured from the solar wind. When these particles strike the top of Earth’s atmosphere (the ionosphere), they dislodge electrons. Electric fields, which form naturally in Earth’s spinning magnetosphere, grab the liberated electrons and accelerate them skyward in collimated beams.

(2) Why don’t the beams ever go away? Short answer: because the solar wind never stops blowing. Even when the sun is quiet, Earth’s magnetosphere is jostled and energized by the ever-present solar wind. As a result, electrons are always being knocked off the top of Earth’s atmosphere as described in Note #1. Although solar storms are not required for this process, solar storms can help. For instance, when a CME strikes Earth’s magnetosphere, the contents of the magnetosphere become extra-energized. Lots of particles furiously strike the top of Earth’s atmosphere, liberating even more electrons than usual. Earth’s electron beams can thus become super-charged. When the storm subsides, the electron beams may weaken, but they never vanish because even the quiet sun produces solar wind.

References:

Zhang, X., Angelopoulos, V., Artemyev, A. V., Zhang, X.-J. (2021), Beam-driven ECH waves: A parametric study, Phys. Plasmas, 28, 072902, https://doi.org/10.1063/5.0053187

Zhang, X., Angelopoulos, V., Artemyev, A. V., Zhang, X.‐J., Liu, J. (2021). Beam‐driven electron cyclotron harmonic waves in Earth’s magnetotail. Journal of Geophysical Research: Space Physics, 126, e2020JA028743. https://doi.org/10.1029/2020JA028743s

https://spaceweatherarchive.com/2021/09/20/earth-can-makes-its-own-auroras/

Solar Minimum is having a calming effect on Earth's magnetic field. The deepening quiet is shown in these geomagnetic data, taken by Stuart Green of Preston, Lancashire, UK, during each of the past 3 summers:

"I've plotted the changing levels of geomagnetic activity for the months of May, June and July (between the equinoxes) for the years 2017, 2018 and 2019," explains Green, who operates a research-grade magnetometer buried in his backyard. "The trend is clearly downward, with less frequent and intense storms in 2019, as the sun continues deeper into Solar Minimum."
His data show why minor G1-class geomagnetic storms, which would rarely be mentioned during Solar Maximum, are suddenly noteworthy. Any magnetic storm is news at this point in the solar cycle.
The quiet won't last forever, though. A panel led by experts from NOAA and NASA predict that the solar cycle will bottom out in late 2019 with a bounce back to higher levels of activity beginning sometime in 2020. Meanwhile, G1 is a significant magnetic storm.
www.spaceweather.com

A minor interplanetary shock wave hit Earth on May 26th at approximately 22:00 UT. The CME-like disturbance was unexpected. It caused the density of the solar wind around Earth to abruptly quadruple, while the interplanetary magnetic field doubled in strength. Minor geomagnetic storms are possible on May 27th as our planet passes through the shock wave's wake.
www.spaceweather.com

When a stream of solar wind hits Earth's magnetic field, magnetometers around the Arctic Circle normally go a bit haywire, with their needles swinging chaotically as the buffeting ensues. Rob Stammes of the Polarlightcenter, a magnetic observatory in Norway, sees such disordered behavior all the time. But on Nov. 18th something quite different happened. The solar wind produced a pure sine wave:

"A very stable ~15 second magnetic oscillation appeared in my recordings, and lasted for several hours," he says. "The magnetic field was swinging back and forth by 0.06 degrees, peak to peak."
Imagine blowing across a piece of paper, making it flutter with your breath. The solar wind can have a similar effect Earth's magnetic field. The waves Stammes recorded are essentially flutters propagating down the flanks of our planet's magnetosphere excited by the breath of the sun. Researchers call them "pulsations continuous" -- or "Pc" for short..
"A sensitive magnetometer is required to record these waves," says Stammes. "I use a mechanical magnetometer with bar magnets suspended from a special wire. LEDs and light detectors in an isolated dark box record the motion of the magnets, while vanes in oil damp out non-magnetic interference."
Pc waves are classified into 5 types depending on their period. The Nov. 18th waves fall into category Pc3. Researchers have found that Pc3 waves sometimes flow around Earth's magnetic field and cause a "tearing instability" in our planet's magnetic tail. This, in turn, sets the stage for an explosion as magnetic fields in the tail reconnect.

A quartet of NASA spacecraft recently flew through just such an explosion. Last week, researchers from the University of New Hampshire reported that four Magnetospheric Multiscale (MMS) spacecraft spent several seconds inside a magnetic reconnection event as they were orbiting through Earth's magnetic tail. Sensors on the spacecraft recorded jets of high energy particles emerging from the blast site. One jet was aimed squarely at Earth and probably sparked auroras when it hit the upper atmosphere.
Stammes has recorded many Pc waves in the past, "but this is the first time I have detected category Pc3," he says. "This was a very rare episode indeed."
www.spaceweather.com

Last weekend, Nov. 10th, a stream of fast-moving solar wind hit Earth's magnetic field, igniting a ring of auroras around the South Pole. Minoru Yoneto saw the red-purple glow all the way from Queenstown, New Zealand:

"We were lucky to catch another Southern Lights display during my stargazing tour," says Yoneta. "Our guests were excited to photograph them using their own cameras."

Queenstown is at 45 degrees south latitude--a considerable distance from the South Pole. That's why the auroras looked red. Auroras circling the South Pole must reach very high above Earth's surface to be visible half a hemisphere away. At altitudes greater than ~200 km, auroras turn red. The ruby glow occurs when high energy particles from space hit oxygen atoms at the top of the atmosphere. Ionized molecular nitrogen adds a dash of purple to the high-altitude palette.

More red Southern Lights are possible on Nov. 18th or 19th when a new stream of solar wind is expected to arrive. The gaseous material is flowing from a relatively small hole in the sun's atmosphere. Queenstown stargazers, charge your cameras!
www.spaceweather.com

The Parker Solar Probe has just radioed NASA with good news. The spacecraft survived its close approach to the sun on Nov. 5th. Because the sun is a giant natural source of broadband radio noise, Parker cannot transmit complicated data streams through the interference. Images and data won't arrive until early December when the probe has reached a sufficient distance from the sun again. For now, mission controllers are happy to have received a simple beacon saying the spacecraft is okay.

Earlier this week, Parker screamed around the sun at 213,200 mph only 15 million miles from the stellar surface--shattering old records for both speed and distance. Intense sunlight raised the temperature of the probe's heat shield to about 820 degrees Fahrenheit. All the while, instruments and systems behind the shield kept cool in the mid-80s F.

Mission controllers at the Johns Hopkins University Applied Physics Lab received the status beacon at 4:46 p.m. EST on Nov. 7, 2018. It indicated, simply, "A" — the best of all four possible status signals, meaning that the probe is operating well with all instruments running and collecting science data and, if there were any minor issues, they were resolved autonomously by the spacecraft. Stay tuned for "first light" science results about one month from now.
www.spaceweather.com

NASA's Parker Solar Probe is now closer to the sun than any other spacecraft in history, shattering the previous record of 26.6 million miles set by the Helios 2 spacecraft in 1976. The probe is now well inside the orbit of Mercury."It's a proud moment for our team," says Project Manager Andy Driesman of the Johns Hopkins Applied Physics Laboratory.

Count to 3. Parker just broke the record again. The spacecraft is accelerating sunward for the mission's first perihelion on Nov. 5th. At closest approach, the solar disk will seem 6 times wider than it does on Earth as the probe is hit by "brutal heat and radiation" (NASA's words). Parker's carbon-composite heat shield is expected to heat up to a sizzling 2000 deg. F.
Parker's prime mission is to investigate the origin of the solar wind--a project best done uncomfortably close to the star. Parker will trace the solar wind back to its source and find out how it escapes the sun's gravity and magnetic confinement.
Russell Howard of the Naval Research Laboratory expects to learn a lot from this encounter. "We might detect magnetic islands in the solar wind, which have been theoretically predicted. And if a CME (solar explosion) happens or a comet passes through the sun's atmosphere while we are so nearby, it could be spectacular."

Howard is the principal investigator for WISPR, the probe's wide-field camera system. WISPR can actually see the solar wind, allowing it to image clouds and shock waves as they approach and pass the spacecraft. Other sensors on the spacecraft will sample the structures that WISPR sees, making measurements of particles and fields that researchers can use to test competing theories.
"We lose communication with the spacecraft during the perihelion period which begins next week," notes Howard. "This is because there isn't sufficient power to drive both the instruments and the transmitter. The first dump of data will occur in early December." Stay tuned for that.
Parker will plunge toward the sun 24 more times in the next 8 years, breaking many records en route. Here's the timeline.
www.spaceweather.com

On Oct. 26th, Venus will pass almost directly between Earth and the sun--an event astronomers call "inferior solar conjunction." As Venus approaches the sun, the planet is turning its night side toward Earth, reducing its luminous glow to a thin sliver. Shahrin Ahmad of Kuala Lumpur, Malaysia, took this picture on Oct. 20th:

"I took this picture in broad daylight," says Ahmad. "Venus was really big in the eyepiece of my telescope--almost a full arcminute in diameter. And the crescent shape easily visible in the 8x50 finder scope."
In the days ahead, the crescent of Venus will become increasingly thin and circular. The horns of the crescent might actually touch when the Venus-sun angle is least (~6 degrees) on Oct. 26th. This is arguably the most beautiful time to observe Venus, but also the most perilous. The glare of the nearby sun magnified by a telescope can damage the eyes of anyone looking through the eyepiece.
Anthony J. Cook of the Griffith Observatory has some advice for observers: "I have observed Venus at conjunction, but only from within the shadow of a building, or by adding a mask to the front end of the telescope to fully shadow the optics from direct sunlight. This is tricky with a refractor or a catadioptric, because the optics start at the front end of the tube. Here at Griffith Observatory, I rotate the telescope dome to make sure the lens of the telescope is shaded from direct sunlight, even through it means that the lens will be partially blocked when aimed at Venus. With our Newtonian telescope, I add a curved cardboard mask at the front end of the tube to shadow the primary mirror."
For the rest of this week Venus can still be observed without elaborate precautions in deep twilight after sunset. Every evening the crescent grows and narrows. Scan the realtime photo gallery for updates.
www.spaceweather.com

The sun is entering a deep Solar Minimum, and Earth's upper atmosphere is responding. Data from NASA's TIMED satellite show that the thermosphere (the uppermost layer of air around our planet) is cooling and shrinking, literally decreasing the radius of the atmosphere. If current trends continue, the thermosphere could set a Space Age record for cold in the months ahead: Full story.
www.spaceweather.co

The Moon is about to take a bite out of the sun. On Saturday, August 11th, there will be a partial solar eclipse visible from locations around the Arctic Circle and across much of Asia. During the 3+ hour event, as much as 73% of the solar disk will be covered. Selected cities in the eclipse zone include Moscow (2.1% coverage), Oslo (4.8%), Raykjavik (20%), Tromso (29%), and Seoul (35%).    www.spaceweather.com

An interplanetary shock wave hit Earth's magnetic field on April 19th around 23:50 UT. When the disturbance arrived, the density of solar wind flowing around our planet abruptly quadrupled and a crack opened in Earth's magnetic field. The resulting G2-class geomagnetic storm sparked unusual "electric blue" auroras. 

"I've been flying airplanes for 20 years and photographing aurora for 10 years, but I've never seen anything like this before" reports pilot Matt Melnyk, who photographed the display from 39,000 feet.  "Electric blue auroras!" he says. "This was while on a red eye flight from Edmonton to Toronto around 4 am over northern Manitoba. Unbelievable sky. I was able to grab some hasty shots with a cell phone."

Auroras are usually green--a sign of oxygen. Rare blue auroras are caused by nitrogen molecules. Energetic particles striking N2+ at the upper limits of Earth's atmosphere can produce an azure glow during intense geomagnetic storms. 

What is an interplanetary shock wave? It is a supersonic disturbance in the gaseous material of the solar wind. These waves are usually delivered by coronal mass ejections (CMEs). Indeed, this one might have been a minor CME that left the sun unrecognized earlier this week.

Alternately, it might have been an unusually sharp co-rotating interaction region (CIR). CIRs are transition zones between slow- and fast-moving streams of solar wind. They contain plasma density gradients and magnetic fields that often do a good job sparking auroras.
www.spaceweather.com

See also: 'Strong New Moon, Solar Activity and Gateways Ahead' by Sandra Walter, Wayshower, Ascension Guide and Gatekeeper

A strong geomagnetic storm was brewing in the skies above Alberta, Canada, on Sept. 27th when photographer Alan Dyer looked up and saw a ribbon of purple light arcing cross the sky. It was the mysterious aurora known as "Steve": 

"The Steve arc appeared for only about 20 minutes, starting at 10:45 pm MDT, during a lull in the main display," says Dyer, who captured the arc in a 6-shot, 360o panorama.For many years, northern sky watchers have reported this luminous form occasionally dancing among regular auroras. It was widely called a "proton arc" until researchers pointed out that protons probably had nothing to do with it. So members of the Alberta Aurora Chasers group gave it a new name: "Steve."
"We seem to be ideally located in the Canadian Prairies for sighting Steve, as we often get the main aurora to our north, placing Steve overhead or to our south," notes Dyer.

No one fully understands the underlying physics of the purple ribbon. One of the European Space Agency's Swarm satellites flew straight through Steve during a previous apparition. Data revealed a relatively hot river of gas, about 25 km wide, flowing rapidly through Earth's outer atmosphere. "Steve seems to be a thermal emission from hot flowing gas rather than from precipitating electrons," says Dyer, "but his origin and nature are still mysterious."  www.spaceweather.com